Appendix D: Summary of Olympia Stream Basin Traits (Source: Aquatic Habitat Evaluation and Management Study, City of Olympia, 1999) After an overview of data sources and overall basin characteristics, this appendix summarizes the available information relevant to the evaluation of aquatic habitat conditions. Data is organized based on functional relationships presented and discussed in the University of Washington research cited in the study report: Basin conditions (extent of development and hydrologic regime) Riparian conditions (integrity of the riparian corridor) Instream and wetland habitat conditions (physical habitat and water quality) Aquatic biota (fish and macro-invertebrates) This information is summarized further in Table 3.2 of the Aquatic Habitat Evaluation and Management Study report. The basins are discussed in order of the rankings described in Section 3.5 of the report. Data Sources Primary data sources consulted for this summary are: Comprehensive Drainage Basin Plans for Indian-Moxlie Creeks (1993), Percival Creek (1993), Woodard Creek (1995), Chambers/Ward/Hewitt (1995), and Green Cove Creek (1998). Basin Reconnaissance and Public Involvement Report (1993), containing information about Mission, Ellis, and Schneider Creeks. Thurston County's Water Quality Monitoring Report for the 1996-97 water year and previous similar reports. Olympia's Wildlife Habitat Study Final Recommendations (1994). Additional information on Olympia’s streams and wetlands presented in biological investigations, watershed plans and research papers. Overview of Creek Drainage Basins Olympia’s eight major drainage basins are shown in Figure 1.1 in relationship to the City limits and Urban Growth Area. Budd Inlet/Deschutes River Watershed Ellis Mission Indian-Moxlie Chambers/Ward/Hewitt Percival Schneider Henderson Inlet Watershed Woodard Eld Inlet Watershed Green Cove D-1 The following summary of basin conditions is excerpted from the Basin Reconnaissance and Public Involvement Study (Olympia 1993). Population and Land Use Thurston County has experienced a steady increase in population since 1900. Before the 1960s, the county’s average growth rate was about 20% per decade. Population has doubled since 1970. The county’s rapid growth has made it the eight most popuous county in the state despite its relatively small size. The current growth trend, spurred by expanding service, trade, and government services, is expected to continue. Growth outside the urban core has accounted for 75% of the area’s new development, most of which can be described as low density urban sprawl. In an effort to restrict sprawl, the Cities of Olympia, Lacey, and Tumwater have delineated an 84-square-mile Urban Growth Area (UGA). Within the UGA, land use policies and infrastructure are designed to encourage high density housing and commercial development; outside the UGA is intended to remain in low density rural use. The majority of the basins included in this report fall within the UGA. Climate The South Puget Sound region has a marine climate typical of the west coast. Summers are relatively dry and cool; winters are mild and wet. Average annual precipitation is about 53 inches. During the wet season, rainfall is usually of light to moderate intensity and continuous over a long period. Typical rainfall is as follows: Approximate Seasonal Rainfall (inches) Fall 10 Winter 29 Spring 10 Summer 4 Major storm events in the Olympia area have been evaluated for the purpose of characterizing stormwater runoff quantities and sizing conveyance and storage facilities. This evaluation generated theoretical design storms that are defined as the precipitation expected in a 24-hour period from a storm of a given recurrence interval. Although precipitation varies with geographic location, the 24-hour rainfall values are used for stormwater facility design throughout northern Thurston County (Drainage Design and Erosion Control Manual for the Thurston Region, 1994). Storm Recurrence Precipitation (years) (inches/24 hours) 2 2.80 5 3.75 10 4.35 25 5.10 50 5.65 100 6.15 D-2 The prolonged wet season in the Puget Sound region presents unique problems in estimating the quantity of runoff generated by a storm of specific intensity and duration. Often the level of moisture in the soil profile immediately preceding a storm event is high. Given a saturated soil, only minimal amounts of precipitation can be infiltrated. The likelihood of high antecedent moisture levels in soils requires extra care when predicting the amount of runoff that can be expected from a storm event. Topography The basins described in this report are located between the mountainous Black Hills on the west and expansive prairies on the east. These basins surround and drain to Budd Henderson, and Eld Inlets, the southernmost points of Puget Sound. Most creeks have low to medium gradients and are often fed by numerous groundwater springs. Most of the creeks have formed deeply incised banks in downstream portions of the channels. In general, land area in the basins is moderately sloped with frequent rolling terraces and occasional small glacial depressions known as kettles. In the southeastern areas, these small depressions often contain lakes, which are groundwater fed and commonly have no surface inlets or outlets. Geology and Soils The geologic history of the Olympia area plays a major role in determining the surface and subsurface drainage characteristics of the basins. Glacial ice from the north entered the South Puget Sound region at least several times. The low topography on the east side of the Olympic Peninsula routed a portion of the progressing glaciers into northern Thurston County. As the glaciers advanced and then retreated, several types of material were deposited in creek channels and lowlands. On the westside of Olympia and to the north, the glaciers left primarily till at the surface, which occurs as gravelly creekbeds providing good habitat for anadromous fish. On the eastside and to the southeast, surface soils are primarily sand associated with the Lake Russell Deposits; this material dominates creek substrate, offering lower quality anadromous fish habitat and resulting in less instream biotic diversity. The Vashon glaciation is of primary importance to local geology. This glacial event receded only 10,000 years ago, after covering the area for 2,000 years. Glacial advancement over existing landforms compacted underlying sand, silt, clay and gravel. The resulting concrete-like material known as glacial till has low permeability and therefore generates considerable stormwater runoff. The tills are fairly stable in slopes. Conversely the material deposited ahead of advancing glaciers by melting ice, known as advance outwash, is composed of highly porous sands and gravels. A second type of outwash, recessional, was formed by retreating glaciers. The outwash soils are deeper and much better drained than the till soils. Outwash materials with a high content of silt and sand are prone to erosion; those that are more sorted and contain larger material are more resistant to erosion. Another soil group, clay, formed during glacial compaction of the fine material deposited in pre- glacial lakes. Wetlands typically contain unique hydric soils. These soils are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions that favor the growth and regeneration of specific vegetative types. D-3 Recent glacial activity also developed a unique land form in what is now the southeast portion of Olympia. Upland depressions known as kettles or potholes were formed by the deposition of materials form the receding Vashon glacier. These depressions re typically closed to surface discharge, steeply sloped, and commonly support wetland vegetation. Critical Areas Critical areas within the basins include wetlands, floodplains, aquifers, shorelines, and geologic formations. Development restrictions apply to many of these areas as delineated on local zoning maps. Wetlands. Wetlands are usually found in low-lying areas where land and water come together. These areas can occur along coastal shorelines, river and stream banks, around the shores of lakes, or in areas fed by underground springs. Wetlands are distinguished by their soil types and vegetation. In wetlands, water is present at or near the surface for extended periods of time during the growing season, thereby affecting the traits of the soils. Only plans adapted to living in these conditions can survive in wetlands. Wetlands provide a number of valuable ecological functions that commonly include water purification, flood control, shoreline stabilization, recharge of groundwater and streams, and wildlife and fish habitat. The headwaters of nearly all the streams in Olympia are located in wetlands. Many of these wetlands have been encroached upon or completely eliminated. Basins located within the highly urbanized areas of Olympia now have only small, if any wetlands remaining. Less developed basins contain larger, more extensive wetlands. Shoreline areas. The basins contain several relatively large lakes, many of which are protected by the requirements of the Shoreline Master Program for the Thurston region. Ward and Hewitt Lakes are designated as rural environments; Chambers is designated as a conservancy environment. Saltwater shorelines in Thurston County are designated as conservancy environments, except for Budd Inlet south of Priest Point Park, which is an urban environment. With the exception of